Using 1.4.7 support build - Zenpage Theme. Found the following problem:

Users with different Users ID but with same email address can both register. e.g.

If there is already a user who has registered with a user id of "user1" and an email of "user1@testmail.com" then a second user can register with a user id of "user2" and the same email as user1 i.e. "user1@testmail.com"

However if the second user also uses the same user id e.g. user1 then the "Registration Failed" Message comes up saying that user ID user1@testmail.com is already in use.

Moreover if the second user uses the same user id i.e. user1 but a different email address e.g. user2@testmail.com then the "Registration Failed" Message comes up saying that user ID user2@testmail.com is already in use which actually is not the case. It should give the message that user ID is already in use.

Indeed the mail addresses should be required to be unique.

ticket created